Engine air/fuel control systems are known in which fuel delivered to the engine is adjusted in response to the output of an exhaust gas oxygen sensor to maintain average air/fuel ratios at a stoichiometric value. Such systems may also include a fuel vapor recovery system wherein fuel vapors are purged from the fuel system into the engine's air/fuel intake. An example of such a system is disclosed in U.S. Pat. No. 5,048,493. When such systems are employed with conventional electronic engine controls systems that adaptively learn and diagnose fuel and air system errors, a conflict occurs. In particular, error learning and diagnosis must be disabled during purging of the fuel vapor recovery system. Similarly, purging of the fuel vapor recovery system must be disabled during learning and diagnosis of fuel and air system errors.
The inventors herein have discovered numerous disadvantages when disabling purging during fuel error learning and when disabling fuel error learning during purging. Specifically, the maximum amount of purging that can be accomplished is substantially limited, requiring larger and more expensive purge systems. Also, sudden fuel error that occur during purging may not be diagnosed.